The Max Planck Institute of Plasmaphysics is building up the stellarator fusion experiment Wendelstein 7-X (W7-X) at the branch institute in Greifswald. W7-X continues the line of stellarator experiments at IPP. To allow for steady state operation W7-X has a superconducting coil system with 50 non-planar and 20 planar coils. The coil system is grouped in five equal modules, each consisting of two mirror symmetric half modules. The half modules are assembled from five different non-planar coils, two planar coils and a sector of the coil support structure. All cryogenic parts are enclosed in a cryostat to protect them from ambient temperature. The magnet system was ordered from the European industry. The production of superconductor, winding packs and encasings are under way. The main focus of this contribution aims on the fabrication state of the coil system.

WENDELSTEIN 7-X, a superconducting fusion experiment, is presently under construction at the Greifswald branch of the Max-Planck-Institut fur Plasmaphysik (IPP), Germany. The magnetic confinement of the plasma is achieved by 70 coils. In case of a rapid shutdown (e.g., caused by a quench) a very reliable protection system has to reduce the current in all coils within seconds. Different concepts applying linear and nonlinear resistors, which operate at room temperature or at 80 K, were studied. To switch the current electronic and mechanical breakers were considered. The paper presents the concepts studied and describes in detail the selected solution.

The stellarator of the Wendelstein 7-X (W7-X) experiment contains a superconducting magnet system comprises 70 coils and a central support structure. The magnet system has been designed with respect to the physics aims of the experiment. Based on these main features, the components have been ordered from European industry. The subsequently detailed design of the single components and recent prototype test results required the modification of some features. The final design of the components is described in the contribution.

In the frame of the W7X stellarator project, a cooperation agreement between the Max-Planck-Institut fur Plasmaphysik and CEA has been set-up in order to perform the acceptance tests of all the 70 superconducting coils that compose the W7X magnet system. The main purpose of these tests is to demonstrate that each coil can work at nominal operating conditions, with enough margin to ensure the coil safety during the stellerator operations. For that purpose, CEA has built a new test facility at Saclay. This paper presents a general overview of the test facility. It is mainly composed of two large cryostats (useful space of 5 m diameter and 4.2 in height), a cryogenic source to produce supercritical helium at 4.5 K and 6 bar with a power rating of 200 W, and an electrical power supply of 25 kA. Each cryostat can contain two coils. It is then possible to cool down two coils at the same time, and to warm up two others. But only one coil can be energized at the same time. As the assembly of the facility is now nearly completed, the first cryogenic tests with the prototype coil (DEMO) have started. The first conclusions of these tests and the facility performances will also be discussed in this paper.

An overview is given on the status of the demo-cryostat project for the WENDELSTEIN 7-X stellarator, Construction and assembly of the prototype are finished, and the test period is near completion. The intention of this project was to get experience with design and construction of W7-X-components, as well as with assembly of this complex system. The goal is now practically achieved, and it could be demonstrated that the W7-X cryostat can be built with reasonable effort. Many of the solutions found can be adopted directly for W7-X, or are starting points for further improvements. A short description is given of the cryostat, its assembly, and of the most important tests which were performed so far. (C) 2001 Elsevier Science B.V. All rights reserved.

The plasma fusion experiment WENDELSTEIN7-X (W7-X) of the stellarator family, which was developed at the Max-Planck-Institute for Plasmaphysik, is in the state of the final detail design. W7-X is planned for first operation in 2006. Currently the main components (coils, magnet support structure, vacuum vessel, …) are ordered to be manufactured. This paper gives a summarization of the development of the magnet support structure during the last 10 years. Of course, the final design and its structural analyses are the main topic of the discussion. Finally, it is tried to summarize the cognitions won until now and based on this knowledge to give the recommendations for future activities.

The superconducting magnet system for the new stellarator WENDELSTEIN 7-X, to be located at Greifswald, Germany, consists of 50 non-planar and 20 planar large magnetic coils. A central support ring carries the coils and keeps them in their geometrical position. Additional lateral stiffening elements between the coil housings together with the support ring, generate a complex 3D-framework system which has to balance the considerable Lorentz forces, typically in the range of 1–5 MN for the single coil and 10 MN residual value for centripetal directions. The paper presents the detailed design of the magnet system, its functional layout for the achievement of the necessary geometrical accuracy, and the elements for the force transmission. The actual status of industrial activities for the realisation of the magnet components is presented and the magnet assembly conditions are discussed.

The Stellarator of the Wendelstein 7-X (W7-X) experiment contains a system of 50 non-planar and 20 planar superconducting coils. The coils were designed by the IPP. The coil manufacturing and inspection is shared between several European enterprises and consortiums. The coils consist of the winding pack embedded in a stainless steel casing and of the related instrumentation. Design details, tolerances and guarantee values and differences between the coils types are described in the contribution. The features of the superconductor are described separately. Finally, the contribution indicates measures adopted by the W7-X project to ensure the quality of the coil design and manufacturing.

Wendelstein 7-X (W 7-X) is a stellarator plasma experiment currently under construction in Greifswald, Germany. It is an advanced stellarator with a magnet system consisting of 50 non-planar superconducting main field coils and 20 superconducting planar auxiliary coils in modular toroidal arrangement. The auxiliary system is foreseen for the variation of plasma parameters which allows extensive plasma studies in wide parameter ranges. The characteristic dimensions of a coil are: 3.5 m in height, 2.5 m in width and 1.0 m in thickness. In order to prove the fabricability and the electromagnetic, thermohydraulic and mechanical performance of the coils, a full-size demonstration coil was built by industry and delivered to the Forschungszentrum Karlsruhe for testing. Here, the coil was prepared for installation at the test facility TOSKA beside the EURATOM LCT coil. This coil delivers a background field which allows the simulation of different load cases occurring later in the experimental device. The aim of the test was the investigation of the mechanical properties and behaviour of the bedding between winding block and casing. In this paper, the electromagnetic results obtained during the test will be presented.

The stellarator Wendelstein 7-X (W7-X) is presently under construction at Greifswald, Germany, and the start of operation is planned in 2006. W7-X is a large `advanced stellarator' of the HELIAS type (R = 5.5 m, a = 0.55 m, B0 = 3 T, five periods, moderate shear and variable rotational transform 5/6 ⩽ ι ⩽ 5/4 at the boundary) with the aims of demonstrating the reactor potential of this stellarator line in steady state operation close to fusion relevant parameters. The capability of stationary operation requires the realization of a superconducting magnet system consisting of 50 modular coils and 20 planar coils, the operation of a 140 GHz ECR CW heat source of 10 MW, the installation of a divertor to handle the power and particle flux, and to limit the impurity fraction to tolerable levels. Additional heating schemes, ICRF and NBI, will be provided for flexible experimentation.

The technical aspects of steady state operation of the W7-X stellarator are outlined. For cwoperation superconducting coils are necessary which are thermally insulated by a cryostat. The ECRH system of W7-X consists of ten gyrotrons with a cw-power of I MW each. ICRH and NBI are used in pulsed mode but can be upgraded for longer pulses. The control system allows a flexible use of the discharges. Diagnostics and data acquisition will handle the data with parallel computation and data reduction before storing. 48 MW of electrical power will be supplied from the mains which can be upgraded to 9l MW. The power supply for the heating is based on pulse step modulators with 3.3 MW cwor 6.5 MW pulsed-power. The magnets are fed by 20 kA, 30 V modules with a fast protection system. The refrigerator is designed for 3.5 kW at 4 K. Large water reservoirs allow a pulse length of 30 min at full power.

WENDELSTEIN 7-X (W7-X) is an optimized advanced stellarator and continues the successful stellarator line of the IPP Garching. w7-X will be built at Greifswald and will exploit the inherent capability of the stellarator principle for stationary operation and aims to demonstrate its basic qualification as a power plant. The technical challenges of the major components of W7-X are being described in detail.

The Wendelstein 7-X Stellarator (W7-X) is the next step device in the stellarator line of IPP Garching. A new branch of IPP is being built at Greifswald, Germany, to house W7-X. The design of W7-X is based on physics principles, which are discussed in the light of experimental results from the W7-AS stellarator. The experiment aims at demonstrating the inherent steady state capability of stellarators at reactor relevant plasma parameters and is therefore equipped with a modular superconducting twisted coil system. The 3D magnetic configuration of W7-X asks for a special divertor solution for steady state heat removal and decoupling of the vessel wall from the plasma. The status of the design and construction of W7-X including heating systems, divertor and diagnostics is presented.

The Helias reactor (HSR) is an extrapolation of the Wendelstein 7-X configuration to reactor dimensions. The major radius is 22 m and the average plasma radius 1.8 m. The magnetic field on the axis is 5 T and the maximum field on the coils 10.6 T, allowing the use of super-conducting coils based on NbTi technology. The coil system, consisting of 50 modular coils, has been optimised using a finite-element stress analysis. The stresses can be kept below present technical limits. The divertor concept makes use of the magnetic islands in the boundary region; a system of target plates is proposed to collect the plasma outflow. Various physics studies - alpha-particle confinement and ignition scenarios - are described. Recent empirical scaling laws of confinement in stellarators have been taken into account. The thermal output of the Helias reactor is about 3500 MW.

The magnet of the WENDELSTEIN 7-X stellarator consists of five modules each containing five types of non-planar coils as presented in Ref. [1]. Two vessel systems outside and inside the toroidal magnet curvature confine the vacuum for cryogenic operation. The shape of the inner vacuum vessel is defined by the geometry between the surface of the plasma and the inside surface of the coils. The subject of this analysis is the test cryostat for W7-X. A buckling analysis has been performed to obtain the critical-load factors. The method used to perform the calculations is described together with some special demands for the post-processing.